Shutter mechanism in a camera

ABSTRACT

A film winding and focal plane shutter cocking mechanism includes a safety gear that has an annular rib secured to one face. A cut out in the rib is engaged by an end of a lever which is moved by a sliding bar when the shutter actuating button is depressed. An interlocking mechanism which is operated by the safety gear prevents movement of the sliding bar again until the film winding and shutter cocking mechanism has been manually actuated to prevent double exposure.

United- States Patent Yamashita et al.

[54] SHUTTER MECHANISM IN A' CAMERA [72] inventors: Keizo Yamashita;Junichi Yokozato; Hideaki Yamamoto, all of Tokyo,

Japan [73] Assignee: Zenza Bronica Kogyo Kabushiki Kaidm, Tokyo, Japan[22] Filed:' Dec. 23, 1969 I 1 Appl. No.2 887,664

[30] Foreign Application Priority Data Dec. 28, 1968 Japan ..43/96097[52] US. Cl. ..95/57, 95/31 FL [51] Int. Cl ..G03b 9/34 [58] Field ofSearch.....95/l0 C, 53 E, 53 EA, 53 EB,

95/57, 31 AC, 31 FL [56] References Cited UNITED STATES'PATEN'IS I2,961,934 11/1960 Hashimoto ..;....9s/57 Sept. 5, 1972 Otani et a1...95/10 3,437,026 8/1969 Espig ..95/ 10 X 3,437,027 4/ 1969 Straub..95/10 X 3,498,195 3/1970 Ono ..95/57 835,127 11/1906 Borsum ..95/57Burgarella ..95/10 C X Primary Examiner-Samuel S. Matthews AssistantExaminer-Michael L. Gellner Attorney-Michael S. Striker [57] 1 ABSTRACTA film winding and focal plane shutter cocking mechanism includes asafety gear that has an annular rib secured to one face. A cut out inthe rib is engaged by an end of a lever which is moved by a sliding barwhen the shutter actuating button is depressed. An interlockingmechanism which is operated by the safety gear prevents movement of thesliding bar again until the film windingfand shutter cocking mechanismhas been manually actuated to prevent double exposure.

5 10 Drawing Figures tuating mechanism associated therewith comes intoplay for attaining the high-speed-shutter speeds.

A further object of the present invention is to provide a shuttermechanism wherein the mechanical contact between the shaft associatedwith the front shutter screen and the hollow shaft or drum'associatedwith the rear shutter screen is eliminated for attaining a positive andaccurate shutter speed even in the case of the slowspeed shutter. I I

A still further object of the present invention is to provide a shuttermechanism which may be used advantag'eously with an electronicsynchronization device.

A still further object of the present invention is to provide a shuttermechanism provided with a shutter button safety means whereby theshutter actuating mechanism does not come into play before completion ofthe film-winding shutter-tensioning operations. I

These and other objects of the invention will be described in thefollowing detailed description and the accompanying drawing showingpreferred embodiments of the present invention.

In the drawing;

FIG. 1 is a perspective view showing the construction of the shuttermechanism according to the present invention; I v

FIG. his a plan view of a gear operatively connected with the frontleading shutter screen;

FIG. 2b is a plan view of a gear operatively connected with the reartrailing shutter screen;

screen 1 is tensioned by belts 6, 6 secured to the bracket arm 5 andcoiled about rolls 7, 7 mounted on a shaft 4 serving simultaneously forguiding the rear shutter screen 2. The latter is coiled about a shaft 9and tensioned by belts 11, 11 secured to a further arm carrying the freeend of the rear shutterscreen 2, and wound on a drum 8 by way of guidewheels 12,12 mounted coaxially with the drum 3. Said drum 8 houses acoil spring, not shown, and is urged normally to rotate clockwise underthe recoiling force of the spring in the same wayas already describedwith reference to front 7 shutter screen 1.

- metal 21 denotes a projection secured to the upper sur- FIG. '3 is ablock diagram of an control circuit for controlling the actuation of therear shutter screen;

FIG. 4 is a chart illustrating the performance characteristics of thecircuit of FIG. 3;

FIG. 5 is a plan view showing an alternative construction of part of therear shutter screen actuating device;

FIG. 6 is an enlarged view of the shafts associated with the front andrear shutter screen;

FIG. 7 is a perspective view of the substantial parts of the safetydevice associated with shutter actuation button;

.FIG. 8 is a plan view showing the safety device as shown in FIG. 7, thedevice being shown in the operative position when the shutter actuationbutton is depressed manually; and

FIG. 9 is a plan view showing the safety device as shown in FIG. 7, thedevice being shown in the operative position wherein the shutteractuation button is released from manual pressure.

Referring now to FIG. 1, a front shutter screen 1 is coiled at one endabout a winding drum 3, and secured at the other end to a arm 5. Thedrum 3 houses a coil spring, not shown, and is urged normally to rotateclockwise under the recoiling force of the spring. Said face of saidgear 20 for cooperation with a detent member 22 secured to the reverseside of said gear 14. Numeral 23 denotes a substantially L-shaped latchmember pivotally mounted at 24 so that the one end thereof may beengaged normally with said projection 21. Numeral 26 denotes an ironarmature secured to the other end of the latch member 23 and adapted tobe attracted towards the electromagnet 27 against the action of spring28 when the electromagnet 27 is energized. Numeral 29 denotes a bentconnecting lever pivoted at 30 and having a projection 29a engageablewith the other end of the latch member 16. The connecting lever 29 isformed with a raised part 29b adapted for cooperation with a mirrordrive unit 31.

The arrangement is such that when the mirror (not shown in the drawing)is raised upwardly by the mirror drive unit 31 the raised part 29b oflever 29 is pressed by the mirror drive unit 31 so as to turn theconnecting lever 29 clockwise.

Switch S is associated with a release lever 32, and switch S isassociated with one end of the lever 29. Switch 8;, is associated withone end of a lever 34 pivoted intermediate its ends and engaged at theother end with a projection 33 on the gear 14. Switch 8., comprises aleaf spring engageable with a pin 36 mounted on the gear 20.

When the release lever 32 is depressed so as to close the switch 8,, itactuates the mirror drive unit 31 which in turn depresses the projection29b on the connecting lever 29. Switch S is used for slow shutteroperation to charge a desired voltage in the time constant circuitincluding R,, C,, so as not to open a transistorized control circuit forthe rear shutter screen after the release lever has released the switch8,.

Switch S is opened at the moment when the front shutter screen 1 startsto move, because of disengagement of the contacting end 17 of the latchmember 16, by depressing the release lever 32 which operates to turn theconnecting lever 29 and resulting rotation of gear 13 incounterclockwise direction.

The switch S is opened when both shutter screens have finished theirmovements.

FIG. 3 shows a transistorized control circuit for the rear shutterscreen whereby the latter may be actuated after the lapse of a certaintime interval from the time of actuation of the front shutter screen 1.Condenser C, is connected to the gate of transistor T, and the abovementioned switch S, is connected in parallel with the condenser C, whichis charged through a variable resistor R, when the switch S, is opened.Resistor R, is mechanically connected with the shutter dial 37, assuggested by a dotted line in FIG. 3.

Condenser C, is connected in series with the resistor R, and thecharging time of the condenser C, may be varied by adjusting theresistor R, to a desired value.

Resistor R is connected to the source of transistor T,. The transistorsT, and T are connected to each other in such a way that the transistor Tis made conductive and the transistor T, is made non-conductive when thepotential difference at the two terminals of the condenser C, is equalto a certain value Vgs. The abovementioned electromagnet 27 is connectedto the collector of transistor T Switch S, is connected in series withthe electric source E and the switch S, which in turn is connected inparallel with the switch S The operation of the shutter mechanism so farshown and described is as follows:

FIG. 1 shows the shutter mechanism in the operative position and theshutter wherein a film is wound and the shutter is charged forphotographing. In the operative position shown in FIGS. 1,, 2a and 2b,switches S,

v and S, are open, while switches S, and S, are closed.

When the release lever 32 is depressed, switch S, is closed. As theswitch S is still in the on position, transistors T, and T are in thecut-off state. Transistor T, is, however, forwardly biased through theresistor R,, so that the electromagnet 27 is energized and the armature26 is attracted magnetically towards the electromagnet 27 together withthe latch member 23. The foremost part 25 of the latch member 23 abutsagainst projection 21 on the gear 20 and the latter is positively lockedagainst rotation.

With the further depression of the release lever 32, the mirrordriveunit 31 comes into play and the mirror, not shown, starts to retreatfrom the light passage.

When the mirror has been completely retracted from the light passage,the mirror drive unit 31 masses against the raised part 29b on theconnecting lever 29 which is moved in the direction of the arrow in FIG.1 clockwise against the force of a spring so that the end of lever 29closes the switch 8,. As the switch S is connected in parallel with theswitch S, associated with the release lever 32, the electromagnet 27 isenergized with the abovementioned clockwise rotation of the lever 29,while the latch member 16 engaging with the pin 29a is turnedcounterclockwise, so that the front shutter screen 1 is now actuated bymeans of pinion 13. With the actuation of the front shutter screen 1,detent member 22 on the gear 14 is moved away from projection 21 on thegear 20. At this time, the projection 21 is still engaged by theforemost part 25 of the latch member 23 and gear 20 thus prevented torotate, so that the rear shutter screen will not be actuated.

With the start of rotation of gear 14, the projection 33 mounted on thelatter is moved away from engagement with the lever 34 associated withthe switch S and the lever 34 is rotated pivotally clockwise for openingswitch 8,, so that the condenser C,in the transistorized control circuitof FIG. 3 is charged. with the current supplied from the current sourceE by way of the variable resistor R When the potential differencebetween the terminals of condenser C, is equal to Vgs, transistor T, ismade conductive and transistor T, is made non-conductive, so that theelectromagnet 27 is now deenergized.

As the capacity of condenser C, and the potential E of the currentsource remain unchanged and the value Vgs is constant, the charging timeof condenser is decided by the change in the resistance of the variableresistor R,. FIG. 4 shows the relation between the changing voltage andcharging time of the condenser C, with the variable resistor R, adjustedto r, and r As will be seen from FIG. 4, when the variable resistor R,,is adjusted to r,, condenser C, is charged to Vgs at 1,. When thevariable resistor R, is adjusted to r,, then the condenser C, is chargedto Vgs at t,. g

It will be seen from FIG. 4 that by adjusting the ohmic resistance ofthe variable resistor R,, on the shutter speed dial, the shutter timemay be set to the desired value. 1

When the electromagnet 27 is deenergized, the latch member 23 is rotatedcounterclockwise under the force of the spring 28 and caused to moveaway from the projection 21 on the gear 20, so that the latter is urgedto rotate counterclockwise and the rear shutter screen 2 actuated bymeans of pinion 19. Upon closure of the shutter, the projection 36mounted on the gear 20 comes into abutting contact with the switch S, sothat the latter is opened and current from the current source E is nolonger supplied to the control circuit for the rear shutter screen. Theabove-mentioned shutter operation cycle may be repeated in the same wayas described above.

As will be apparent from the foregoing, the energization time of theelectromagnet 27 forming part of the rear screen actuating mechanism maybe adjusted as desired by the on-off performance of the switch means S,to S, associated with the release lever and the mirror drive unit aswell as the front shutter screen, so that the operation of the shuttermechanism may be made positive and accurate as compared with theconventional mechanical control device.

The various shutter speeds may he graduated as desired on the shutterspeed dial in accordance with the position on the variable resistor R,,so that the shutter time adjustment may be attained in a highly simplemanner. The shutter mechanism as disclosed in the present applicationmay be advantageously employed as a focal plane shutter which may bemounted on a large-sized, medium or small-sized camera.

FIG. 5 shows the detailed construction of the latch member 23 and theprojection 21 on the gear 20 associated with the latch member 23. Aswill be seen from FIG. 5, the foremost engaging part 25 of the latchmember 23 is cut obliquely at an acute angle a with respect to thetangential direction of the gear 20. In the similar way, the projection21' on the gear 20 is cut obliquely at the same angle and so as to forman inclined surface 21 contactable with the obliquely cut foremost part25 of the latch member 23.

When the electromagnet 27 is energized, and the foremost engaging partof the latch member 23 engages with the correspondingly inclined meetingsurface 21' on the projection 21, the rear shutter screen 2 cannot beactuated. At this time, a component P is acting tangentially and acomponent 0 is acting radially on the foremost part 25 of the latchmember 23. When the electromagnet 27 is deenergized after a certain timeinterval following the actuation of the front shutter screen, the latchmember 23 is pivoted about shaft 24 under the recoiling force of thespring 28. In this way, the foremost part 25 of the member 23 is movedaway from engagement with the inclined meeting surface 21' formed on theprojection 21.- Thus, the gear 6 is urged to rotate and the rear shutterdiaphragm 2 is now set into motion.

As will be seen from FIG. 5, the said inclined face 21' on theprojection 21 abuts with pressure on the foremost engaging part 25 ofthe latch member 23. As long as the projection 21 engages with theforemost engaging part 25 of the latchmember 23, the component Q actsfor releasing the latter from its engagement with the projection 21.When the electromagnet 27 is deenergized, the component 0 acts in such away that the latch member '23 may be readily set into rotation as if thespring 28 were not provided and the rear shutter screen may be actuatedin synchronism with the deenergization of the electromagnet 27.

FIG. 6 shows a detailed construction of the guide shaft 4 for rearscreen 2 and rollers 7, 7 mounted on the guide shaft 4. In FIG. 6, thebearing means 38, 38 are formed integral with tubular parts 39, 39,. andthe hollow shaft 4 formed into a drum 4a is rotatably mounted on thetubular parts 39, 39 through the bearing means, not shown. A spindle 4bis passed through the hollow inside space of the guide shaft 4 andsecured at either endsto the rolls 7, 7. The said spindle 4b abuts onthe inner peripheral faces 39b,39b of the tubular parts 39,

39. Pinion 13 is secured to the extreme leftward part of the spindle 4b.

When the shutter is released,belts 6, 6 are reeled out with rotation ofthe rolls 7, 7 secured to the spindle 4b, which is rotated axially insliding contact with the outer peripheral faces 39a, 39a of the bearingmeans 38, 38. As will be realized from FIG. 6, there is no directmechanical contact between the spindle 4b and the drum 40 so thatactuation of the front and rear screens may not be adversely affected bythe frictional contact of the moving parts associated therewith and theshutter speed fluctuations may be positively avoided. The number ofcomponent parts may also be reduced and the camera may be miniaturized.

In FIGS. 7-9, there is shown a shutter safety device whereby fool-proofoperation of the shutter mechanism may be attained. Numeral 40 denotes asliding bar for pressing the shutter button and numeral 41 is a gear 41meshing with a gear 43 connected to 'an operating handle adapted forfilmwindin g and shutter-cocking operation. An annular rib 44 is formedon the upper surface of the gear 43 concentrically therewith and cut outat 45 for interlocking with the end 46 of trifurcated lever 46 pivotallymounted at 47. The end 46" of the lever 46 is associated with a spring48 which acts for turning the lever 46 about pivot 47 in such a way thatthe end 46' is moved away from engagement with the cut-out part 45 ofthe rib 44. The end 46" of the lever 46 engages with the foremost partof the abovementioned sliding bar 40. An 'L-shaped lever 49 is pivotallymounted at 51 and is urged to rotate counterclockwise under the force ofspring 52., into abutting contact with a projection 50 on theabovementioned sliding bar 40. An L-shaped detent'lever 53 is formedwith a stop pin 54 which may be engaged by the slanted end edge49' orthe hook surface 49" of the lever 49. The foremost part of the arm 53aof the detent lever 53 is arranged so as to abut the end part of theupright flange 40' mounted on sliding bar 40 or to slide on the lateralsurface of the flange 40'. The other arm 53b of lever 53 is so arrangedand designed so as to abut a stop pin 57 mounted on the camera housingunder the force of spring 56, while the foremost part 53'b thereof restson the rib 44. v

Numeral 58 in the drawing denotes a release pin projecting from theshutter safety gear 41 inside of the annular rib 44, numeral 59 denotesa guide pin engaging in a slot 66 of and guiding the abovementionedsliding bar 40, numeral 61 denotes a movable stop associated with thefilm winding mechanism in such a way that the stop 61 is moved to theleft when the'film is wound in a manner not forming part of the presentinvention, but it may beshifted to the position shown by chain-dottedline before the film is wound'up, so as to retard the movement of thetrifurcated lever 46 and hence the operation of the shutter actuationmechanism.

In the above-described construction, when the handle 42 is turnedmanually for one or two revolutions of the gear 41, and the'film woundup, the annular rib 44 mounted on the gear 41 comes to a halt with thecutout part 45 thereof in facing relation with the end 46' of thetrifurcated lever. 46 as shown in FIG. 7. The shutter button is thendepressed, and the bar 40 associated therewith is moved towards the leftand viewed in FIGS. 7-9 and urges the end 46" of the lever 46 towardsthe left in FIG. 7. As the movable stop 61 is shifted to the full-lineposition as shown in FIG. 7, the lever 46 is free to rotate about shaft47, thus allowing for depression of the release button. The sliding bar40 is free to move towards the left in FIG. 7 and the shutter mechanismcomes into play, as will be seen by referring to FIG. 8 showing theoperative position of the shutter mechanism depicted above. When the.shutter operation is brought to an end, shutter button is released frommanual pressure. Then, the lever 46 is returned to the initial positionunder the force of spring 48, and the sliding bar 40 is also returned tothe initial position. In this situation, the hook face 49" on the lever49 is engaged with the stop pin 54 on the lever 53 so that the slidingbar 40 is locked and the shutter actuating mechanism does not come intoplay evenif the shutter button is depressed manually, as will berealized by referring to FIG. 9 showing the operative position of theshutter mechanism depicted above.

The movable stop 61, on the other hand, is shifted to the chain-dottedline in FIG. 7, as the film is not yet wound.

When the handle 42 is turned manually in the abovementioned way forfilm-winding and shutter-changing operation, the arm 53b of the L-shapedlever 53 is turned by the engagement thereof with the release pin 58 sothat the foremost part of the arm 53a on the L- shaped lever 53 isdisengaged from its abutting contact with the end part of the flange 40on the sliding bar 40 and the lever 53 is restored to the position asshown in FIG. 7.

It will be appreciated from the foregoing description that the shuttermechanism does not come into play while the film is wound up, while therelease button can not be depressed following the release operation, andthe film-winding operation is prevented from its occurrence as long asthe shutter button is depressed manually. Thus, the occasional errors inthe operation of the shutter mechanism such as double exposure may beobviated in a positive manner. The shutter mechanism embodying theabovementioned feature may be fitted on the expensive camera adapted foruse with a so-called removable film pack.

What is claimed is:

1. in a shutter mechanism for a camera, a combina-. tion comprising, afilm winding and shutter cocking mechanism including a safety gearhaving a pair of opposite end faces and an annular rib coaxial with saidgear secured to one of said end faces and provided with a radiallyextending. cutout; lever means movable between an active position inwhich one end of said lever means is engaged in said cutout and aninactive position; biasing means cooperating with said lever meansandztending to maintain the latter in said inactive position; a slidingbar shiftable upon depression of a shutter button from a rest to anadvanced position in which said sliding bar engages said lever means tomove the latter against the force of said biasing means to said activeposition; interlocking means cooperating with said sliding bar duringmovement thereof from said rest to said advanced position and back tosaid rest position for preventing the latter to move again to saidadvanced position before operation of said film windingandshuttercocking mechanism; and means on said safety gear cooperating withsaid interlocking means for releasing said sliding bar during operationof said film winding and shutter cocking mechanism so that said slidingbar may again be moved from said rest to said advanced position thereof.

2. A shutter mechanism for a camera comprising, in combination, a frontscreen and a rear screen; a release lever; a normally open switchassociated with said release lever to be closed when said release leveris actuated; means cooperating with said release lever for startingoperation of said front shutter screen upon actuation of said releaselever; a current source; a transistorized control circuit for control ofmovement of said rear screen, said control circuit comprising acondenser, a normally open switch in parallel with said condenser-andassociated with said front screen to be opened upon actuation of thelatter, and an adjustable resistor in circuit with said condenser; anelectromagnet connected to said control circuit so as to be deenergizedafter elapse of a charging time at which said condenser is charged to apredetermined potential, which charging time varies with the adjustmentof said adjustable resistor; means cooperating with said electromagnetfor starting operation of said rear screen upon deenergizing of saidelectromagnet; a film winding and shutter cocking mechanism including asafety gear, having a pair of opposite faces and an annular rib coaxialwith said gear secured to one of said faces and provided with a radiallyextending cutout; lever means of said lever means is engaged in saidcutout and an inactive position; biasing means cooperating with saidlever means and tending to maintain the latter in said inactiveposition; a sliding bar shiftable upon depression of a shutter buttonfrom a rest to an advanced position in which said sliding bar engagessaid lever means to move the latter against the face of said biasingmeans to said active position; interlocking means cooperating with saidsliding bar during movement thereof from said rest to said-advancedposition and back to said rest position for preventing the latter tomove again to said advanced position before operation of said filmwinding and shutter cocking mechanism; and means on said safety gearcooperating with said interlocking means for releasing said sliding barduring operation of said film winding and shutter cocking mechanism sothat said sliding bar may again be moved from said rest to said advancedposition thereof.

3. A shutter mechanism as defined in claim 2, and including a roll onwhich said rear screen is wound and pulling means tending to pull saidrear screen off said roll, and said means cooperating with saidelectromagnet for starting operation of said rear screen comprising arotary member to be driven by said roll, a projection fixed to saidrotary member and havingan engaging face extending at an acute anglewith respect to a plane including the axis of rotation of said rotarymember and intersecting said face midway between said ends thereof, anda double-armed lever turnably about an' axis intermediate its ends andhaving at one end a face engaging said engaging face to thereby stoprotation of said rotary member and therewith actuation of said rearscreen, an armature on the other end of said lever .and cooperating withsaid electromagnet, when the latter is energized, for holding said faceon said one end of said lever in engagement with said engaging face, andspring means cooperating with said lever for turning the. same in adirection disengaging said face thereof from said engaging face upondeenergization of said magnet. j

4. A shutter mechanism as defined in claim 2, and including amirrordrive actuated by said release lever, a second normally open switchconnected in parallel with said first-mentioned normally open switch andtogether with the same connected in series with said current source,said second normally open switch being associated with said mirror driveand moved to the closed position upon actuation of said mirror drive.

5. A shutter mechanism as defined in claim 2, wherein said rear screenhas a rear part wound about a wind up drum and a leading edge laterallyspaced from a said drum, and including a guide drum for guiding saidrear screen between said wind-up drum and said leading edge on the outerperipheral surface of said guide drum, a spindle extending axiallythrough said guide drum spaced from the inner surface thereof, meansmounting said spindle for rotation about its axis, bearing meansmounting said guide drum on said spindle for rotation relative thereto,and a pair of rollers fixed to opposite ends of said spindle forrotation therewith, said front screen having a trailing edge andincluding a pair of spaced belts each connected at one end to saidtrailing end of said front screen and at the opposite end to arespective one of said rollers.

movable between an active position in which one end

1. In a shutter mechanism for a camera, a combination comprising, a filmwinding and shutter cocking mechanism including a safety gear having apair of opposite end faces and an annular rib coaxial with said gearsecured to one of said end faces and provided with a radially extendingcutout; lever means movable between an active position in which one endof said lever means is engaged in said cutout and an inactive position;biasing means cooperating with said lever means and tending to maintainthe latter in said inactive position; a sliding bar shiftable upondepression of a shutter button from a rest to an advanced position inwhich said sliding bar engages said lever means to move the latteragainst the force of said biasing means to said active position;interlocking means cooperating with said sliding bar during movementthereof from said rest to said advanced position and back to said restposition for preventing the latter to move again to said advancedposition before operation of said film winding and shutter cockingmechanism; and means on said safety gear cooperating with saidinterlocking means for relEasing said sliding bar during operation ofsaid film winding and shutter cocking mechanism so that said sliding barmay again be moved from said rest to said advanced position thereof. 2.A shutter mechanism for a camera comprising, in combination, a frontscreen and a rear screen; a release lever; a normally open switchassociated with said release lever to be closed when said release leveris actuated; means cooperating with said release lever for startingoperation of said front shutter screen upon actuation of said releaselever; a current source; a transistorized control circuit for control ofmovement of said rear screen, said control circuit comprising acondenser, a normally open switch in parallel with said condenser andassociated with said front screen to be opened upon actuation of thelatter, and an adjustable resistor in circuit with said condenser; anelectromagnet connected to said control circuit so as to be de-energizedafter elapse of a charging time at which said condenser is charged to apredetermined potential, which charging time varies with the adjustmentof said adjustable resistor; means cooperating with said electromagnetfor starting operation of said rear screen upon deenergizing of saidelectromagnet; a film winding and shutter cocking mechanism including asafety gear, having a pair of opposite faces and an annular rib coaxialwith said gear secured to one of said faces and provided with a radiallyextending cutout; lever means movable between an active position inwhich one end of said lever means is engaged in said cutout and aninactive position; biasing means cooperating with said lever means andtending to maintain the latter in said inactive position; a sliding barshiftable upon depression of a shutter button from a rest to an advancedposition in which said sliding bar engages said lever means to move thelatter against the face of said biasing means to said active position;interlocking means cooperating with said sliding bar during movementthereof from said rest to said advanced position and back to said restposition for preventing the latter to move again to said advancedposition before operation of said film winding and shutter cockingmechanism; and means on said safety gear cooperating with saidinterlocking means for releasing said sliding bar during operation ofsaid film winding and shutter cocking mechanism so that said sliding barmay again be moved from said rest to said advanced position thereof. 3.A shutter mechanism as defined in claim 2, and including a roll on whichsaid rear screen is wound and pulling means tending to pull said rearscreen off said roll, and said means cooperating with said electromagnetfor starting operation of said rear screen comprising a rotary member tobe driven by said roll, a projection fixed to said rotary member andhaving an engaging face extending at an acute angle with respect to aplane including the axis of rotation of said rotary member andintersecting said face midway between said ends thereof, and adouble-armed lever turnably about an axis intermediate its ends andhaving at one end a face engaging said engaging face to thereby stoprotation of said rotary member and therewith actuation of said rearscreen, an armature on the other end of said lever and cooperating withsaid electromagnet, when the latter is energized, for holding said faceon said one end of said lever in engagement with said engaging face, andspring means cooperating with said lever for turning the same in adirection disengaging said face thereof from said engaging face upondeenergization of said magnet.
 4. A shutter mechanism as defined inclaim 2, and including a mirror drive actuated by said release lever, asecond normally open switch connected in parallel with saidfirst-mentioned normally open switch and together with the sameconnected in series with said current source, said second normally openswitch being associated with said mirror drive and moved to the closedposition upon actuation of said miRror drive.
 5. A shutter mechanism asdefined in claim 2, wherein said rear screen has a rear part wound abouta wind up drum and a leading edge laterally spaced from said drum, andincluding a guide drum for guiding said rear screen between said wind-updrum and said leading edge on the outer peripheral surface of said guidedrum, a spindle extending axially through said guide drum spaced fromthe inner surface thereof, means mounting said spindle for rotationabout its axis, bearing means mounting said guide drum on said spindlefor rotation relative thereto, and a pair of rollers fixed to oppositeends of said spindle for rotation therewith, said front screen having atrailing edge and including a pair of spaced belts each connected at oneend to said trailing end of said front screen and at the opposite end toa respective one of said rollers.